P90X is just awesome and a complete system, yes it can be very hard at times, but if you stick to it very rewarding.

I cannot really do any pulls ups, i can use the bands, so there is always a different way to do things that will enable you to progress and get better, different way to do push ups and more.

You don't need to lift heavy couple of dumbells will work fine, some resistance bands and a yoga mat is all you really need.

I am not sure how low carbing and P90X go? this program is very intense, and when i am in ketosis i simply don't have energy at all?